Unpacking A Conceptual Lesson:
The Case of Dividing Fractions
Randolph A. Philipp
Center for Research in Mathematics and Science Education1
and
School of Teacher Education
San Diego State University
Abstract
A conceptual lesson is presented to help teachers understand why one can invert and
multiply to divide fractions. The topic was chosen not because I argue for the value of teaching
fractions but because it is a topic that most teachers understand only instrumentally and because
understanding the relationships among fractional quantities requires multiplicative reasoning, the
cornerstone to proportional reasoning. Fractions are introduced via pattern blocks, and ways to
connect the physical models to symbolic representations in combining and separating fractional
quantities are explored, with special attention to common confusions between multiplication and
subtraction situations. Lesson excerpts and vignettes contrasting a first grader's beginning
conceptual understanding of fractions with a fifth grader's procedural view that illustrates a lack
of such understanding serve to illustrate three principles for teaching for conceptual
understanding of mathematics: the importance of identifying and attending to the main
mathematical concepts in a topic, building on existing knowledge, and introducing symbols and
procedures after introducing the concepts they represent.
1
Philipp, R. A. (2000). Unpacking a conceptual lesson: The case of dividing fractions.
Center for Research in Mathematics and Science Education, San Diego State University:
San Diego, CA.
A Conceptual Lesson
2
Unpacking a Conceptual Lesson: The Case of Dividing Fractions
Why, when dividing fractions, do we invert and multiply? If you are not able to provide
a clear explanation, you are not alone. Secondary and elementary preservice teachers have
difficulty explaining this procedure (Ball, 1990; Borko et al., 1992). I have found that virtually
none of my preservice elementary and secondary school teachers can provide a conceptually
oriented explanation,2 and after experiencing the lesson outlined below, many of them wonder
why they were never provided an opportunity to make sense of fractions when they were
students.
I first outline a conceptual lesson designed to help students understand division of
fractions, culminating with an explanation for why, when dividing fractions, we invert and
multiply. I recognize that many teachers reading this article will never teach fraction division,
and many may not particularly care why the invert-and-multiply rule works. I chose this topic
not for its intrinsic importance but because it is one that most teachers understand only
instrumentally; that is, they know how to apply the procedure without understanding why the
procedure works (Skemp, 1978). People at all levels can work with fractions, but probably few
people could provide a conceptual explanation for many of the procedures associated with
fractions. The topic of fractions, then, is an example of the notion that given almost any topic,
everyone understands something and no one understands everything, and therefore a key to
effective instruction is to find out what knowledge students possess and to build on that
knowledge. Furthermore, although learning how to divide fractions may not be critical, learning
about the relationships among fractional quantities (e.g., Which is larger, 1/6 or 1/8? How many
times as large?) is part of multiplicative reasoning, which in turn is the cornerstone to learning to
reason proportionally.3
The lesson described here is detailed, because it is in the details that one can see the
importance of focusing on the conceptual ideas of the mathematics and on the students’ thinking
about the mathematics. Finally, when I unpack the lesson and consider key components, I hope
that readers will see implications for mathematical topics they teach.
From Pieces to Fractions
For this lesson with preservice teachers, I generally begin with pattern blocks: a
hexagon; a trapezoid, equal in area to half a hexagon; a rhombus, equal in area to one third of a
hexagon; and a triangle, equal in area to one sixth of a hexagon (see Figure 1). I first ask
students to consider the yellow hexagon to be one whole, and I ask them to construct one whole
in as many ways as they can, provided that they use the same-sized pieces for each whole (see
Figure 2). We discuss the fact that because two red trapezoids make one whole, each red
trapezoid is one half of a whole. Similarly, each blue rhombus is one third of a whole, and each
2
Some of my secondary students attempt to explain division of fractions with an
algebraic approach: They show that a/b ÷ c/d can be thought of as a complex fraction
(a/b) / (c/d), and then they multiply the complex fraction by 1 in the form of (d/c) / (d/c)
resulting in (a/b x d/c) / 1. I am always left with the question: “Of what is this a proof,
and for whom?”
3
By reason proportionally, I do not refer to ability to set up a proportion a/b = c/d and
solve for the unknown. Instead I refer to ability to, for example, compare the growth of
two snakes, one that grew from 4’ to 7’ and the second that grew from 5’ to 8’, by
recognizing that the growth of the smaller is 3/4 of its original size whereas the growth of
the larger is only 3/5 of its original size.
Philipp
3
4
green triangle is one sixth of a whole. We discuss several key aspects of this area model of
fractions at this point. First, to create fractional parts, we must partition the whole so that the
pieces within each partitioning are of equal size. Second, the entire whole must be “used up.”
Third, the more equal-sized parts into which the whole is partitioned, the smaller each part is.
Finally, we are able to connect notation to these pieces, so that, for example, each of the six
green triangles can be represented as 1/6 of the whole.
Figure 1. Pattern blocks.
4
In a set model not all parts of the whole are of equal size. In finding 1/4 of a set of 12
people, the number of people, not their sizes, is the important factor.
A Conceptual Lesson
4
Figure 2. Making one whole with same-sized pieces.
Combining and Separating Portions
At this point students should connect the physical model to the symbolic representation
(Wearne & Hiebert, 1988). That is, when students see one red trapezoid, they hear in their mind’s
ear “one half” and can picture in their mind’s eye the symbol 1/2. After they make these
connections, students are able to represent one whole without using the same-sized pieces (e.g., see
Figure 3 for three common representations), and they can comfortably move among the physical,
verbal, and symbolic representations. We discuss the fact that we can construct many
equivalences without resorting to determining common denominators (see Figure 4).
Figure 3. Representations for one whole composed of different-sized pieces.
Philipp
5
Figure 4. Equivalencies.
When students become comfortable connecting the physical model with the symbolic
representation, I begin posing exercises for them. For example, I ask them to show me 1/2 + 1/3.
Most students solve this by placing the half (red trapezoid) next to the third (blue rhombus, see
Figure 5.1), arriving at an answer of five sixths either by noting that this amount is equivalent to
five greens, or 5 sixths (see Figure 5.2), or by noting that inasmuch as the sum is one green (or
1/6) less than one whole, it equals 5/6 of a whole.
6
A Conceptual Lesson
1
1
Figure 5.1. Show 2 + 3 .
1
1
Figure 5.2. Students’ strategies for adding 2 + 3 .
After posing another addition problem, I ask students to show me 1/2 – 1/3. Students
generally solve this problem by representing 1/2 with one red trapezoid and noticing that one
green (1/6) plus one blue (1/3) is equivalent to one red (1/2). Students then remove 1/3 by
removing the blue rhombus, leaving one green triangle, or 1/6.
Pie, Anyone?
After the preservice teachers work on the task of finding 1/2 – 1/3 using pattern blocks, I
ask them to construct a real-life story problem that might be modeled with the expression 1/2 –
1/3. I find that many preservice teachers have trouble constructing a real-life problem, so after
the students have thought for a few minutes I might provide them a hint by suggesting that they
consider pies. I then ask students to share the problems they have written. I most recently did
this activity with elementary school teachers who experienced difficulty constructing a problem
within 5 minutes, so I told them that recently someone had suggested the following problem5:
5
The following story problem is mathematically equivalent to the “subtraction” problems
written by most of my elementary and many of my secondary preservice teachers. Some
of my students continue to write this type of problem, even after spending several lessons
discussing fractions.
Philipp
7
Pat has one half of a pie left in the refrigerator. For lunch Pat eats one third of the pie.
How much pie does Pat have left?
We have a nice discussion about this problem, because some students think that this story
problem can be represented by 1/2 – 1/3, whereas others are concerned that it is not clear
whether Pat eats one third of the remaining pie or one third of a whole pie. This is precisely the
point I intend to raise with this problem, and we discuss the difference. Some students struggle
with attending to the unit, and I find that they are helped by modeling the situation using the
pattern blocks. If they represent half of a pie with one red trapezoid, then how much pie did Pat
eat? Did Pat eat one third of half of a pie (one green, which is 1/6 of a whole), or did Pat eat one
third of a whole pie (one blue, which is 1/3 of a whole)? They come to recognize that to be more
exact, I should have written the following problem:
Pat has one half of a pie left in the refrigerator. For lunch Pat eats one third of one
(whole) pie. How much pie does Pat have left?
The discussion at this point turns to the reason the expression 1/2 – 1/3 was relatively easy to
work with, whereas this story problem was confusing. We discuss the fact that, on the one hand,
implicit in addition or subtraction is the fact the unit is the same for each term. That is, in the
expression 1/2 – 1/3, the 1/2 and the 1/3 each refer to the same unit. On the other hand, in the
first story problem I wrote, the 1/2 and the 1/3 do not refer to the same unit; the 1/2 refers to one
half of one whole pie, but the 1/3 refers to one third of one half of a pie. I emphasize that this is
the critical distinction that sets addition and subtraction apart from multiplication. We may think
of 4 x 3 as representing 4 groups of 3. In this case, the 3 refers to 3 whole units, but the 4 refers
to 4 groups of 3 whole units. In addition and subtraction, however, we generally do not state the
unit because it is implicit that the unit is the same for all addends: 4 + 3 refers to “4 wholes plus
3 wholes of the same thing.” I sometimes tell my students that multiplication is "gossip math,"
whereas addition and subtraction are not, because in 4 x 3, the 4 is talking about the 3—that is,
the 4 refers to the number of 3s—whereas in 4 + 3, neither number is referring to the other, but
instead both refer to some inferred whole.
Next I ask the students to show me 1/3 of 2 1/2. Figure 6 shows one approach students
take to this task. By representing 2 1/2 with greens, or sixths, they show the 15 sixths in 2 1/2,
and one third of 15 sixths is 5 sixths. After some students explain their solutions to this task, I
ask them to show me 2 1/2 of 1/3. This is very difficult for the majority of my elementary
preservice teachers, and moderately difficult for some secondary preservice teachers. The most
popular solution provided for this problem involves noticing that 2 1/2 thirds is two thirds plus
half of a third (See Figure 7.)
When discussing these two tasks, we note that although 1/3 x 2 1/2 and 2 1/2 x 1/3 are
equal by the commutative property of multiplication, people generally think of “1/3 of 2 1/2”
very differently from the way they think of “2 1/2 thirds.” We conclude that commutativity of
conceptual situations does not even exist.
A Conceptual Lesson
2
1
is the same amount as 15 sixths (or 15 greens).
2
1
1
of 2 is the same
3
2
amount as 5 sixths (or 5 greens).
Therefore,
1
1
Figure 6. A student’s solution for 3 of 2 .
2
8
Philipp
9
2
1
thirds is the same amount as 5 sixths (or 5 greens).
2
1
Figure 7.1. A student’s representation for 22 thirds.
2
1
thirds is the same amount as 5 sixths (or 5 greens).
2
1
Figure 7.2. Another student’s representation for 22 thirds.
Time to Cook
Next I tell the students that we are going to do some cooking. I ask them to consider a
situation:
A recipe calls for 1/2 cup of sugar and you have 1 1/2 cups of sugar in the pantry. If you
have unlimited supplies of the other ingredients, how many recipes could you bake?
Most students immediately see this as three recipes, because there are 3 halves in 1 1/2. Next I
might ask them to consider the same problem situation, but now the recipe calls for 1/3 cup of
sugar, and they have 2 1/3 cups. Again they notice that there are 7 thirds in 2 1/3. I then ask
them to imagine that the recipe again calls for 1/3 cup of sugar, but this time they have 1 1/2
cups of sugar. This problem is identical in structure to the previous two problems, but changing
the values involved makes it possible to focus on a key issue: How do we treat the remainder?
Some students respond that they could make 4 recipes and would have 1/6 cup of sugar left over.
This answer is mathematically correct, but if I leave it there, the students would not think
through a critical idea: that 1/6 cup of sugar is, simultaneously, 1/2 a recipe. We discuss the fact
that 1/6 cup of sugar can be viewed as 1/6 of something and 1/2 of something else (see Figure 8).
10
A Conceptual Lesson
1
1
Figure 8. The remaining sugar can be viewed as 6 cup or 2 recipe.
I follow this problem with the following:
Cynthia would like to bake cookies. She has one cup of sugar in the pantry. How many
batches of cookies can she make using the one cup if each batch requires
A) 1/2 cup
B) 1/3 cup
C) 2/3 cup D) 3/4 cup
E) 4/5 cup.
Students have no problems with the first two situations, which have no remainder, but they have
to think harder about the last three. Problem C can be represented using the pattern blocks, and
the students have to recognize that the 1/3 cup leftover is half a recipe, so Cynthia can bake 1 1/2
recipes. I suggest that the students consider an alternate representation for Parts D and E, and I
draw a picture of a rectangle to represent the cup of sugar. When considering how many recipes
could be baked if each required 3/4 of a cup of sugar, we discuss the picture in Figure 9. The
students who struggle with this have trouble simultaneously viewing one segment as 1/4 of a cup
of a sugar and 1/3 of a recipe. When the students work Problem E, they again have to consider
the fact that 4/5 cup of sugar is equivalent to 1 recipe, and the part left over is simultaneously 1/5
of a cup of sugar and 1/4 of a recipe (see Figure 10).
1
1
Figure 9. The remaining sugar can be viewed as 4 cup or 3 recipe.
Philipp
11
Use the picture at the left to explain
why 1÷ 4/5 = 5/4.
Figure 10. Four-fifths cup of sugar is equivalent to 1 recipe, and the part left over is
simultaneously 1/5 of a cup of sugar and 1/4 of a recipe. Adapted from Thompson, P. W.
(1995). Notation, convention, and quantity in elementary mathematics. In J. T. Sowder
& B. P. Schappelle (Eds.), Providing a foundation for teaching mathematics in the
middle grades (pp. 199–221). Albany, NY: State University of New York Press.
I next ask the students how they would represent Cynthia’s baking problems using
symbolic notation. Are they addition, subtraction, multiplication, or division problems? After
some discussion, the students recognize these as division problems, and I point out that these
division problems are measurement or quotitive division problems, which are different from
partitive or sharing division problems. To use a whole number example, 12 ÷ 3 can be
conceptualized as “How many groups of 3 are there in 12?”—a measurement-division problem.
Compare that to “If we divide 12 into 3 equal groups, how many are in each group?”—a
partitive-division problem. It has been found that children in kindergarten can successfully solve
these problems, but their solution strategies for the two types of problems differ (Carpenter,
Ansell, Frank, Fennema, & Weisbeck, 1993). In the first case, young children directly model the
problem by counting out 12 objects and then taking out groups of 3. The answer is the number
of groups. In the second problem, young children directly model by counting out 12 objects,
then sharing the 12 objects among three fictitious people, often “dealing out” the 12 one-by-one
until they are all shared. The answer is not the number of groups, but instead is the size of each
group.
If you think about these two cases, I think it will become clear that it is difficult to
conceptualize 1 ÷ 4/5 using a partitive model. How might we share 1 cup of sugar among 4/5
people? For fraction situations, it is often more meaningful to use a measurement model: If we
had 1 cup of sugar and each recipe called for 4/5 cup of sugar, then how many recipes could we
bake?
Our thinking might be “One whole has one 4/5 with 1/5 of a whole left over. But that 1/5
of a whole is 1/4 of a 4/5, so one whole has 1 1/4 four fifths.”
Here I like to point out a pattern in the problems we have already solved:
1 ÷ 1/2 = 2/1
1 ÷ 1/3 = 3/1
1 ÷ 2/3 = 3/2
1 ÷ 3/4 = 4/3
1 ÷ 4/5 = 5/4
We notice that the answer to “How many A/Bs are there in 1?” is always “B/A.” We
conceptualize additional tasks, like 1 ÷ 5/6 and 1 ÷ 3/7, until everyone seems comfortable with
the notion that the reciprocal of a number tells how many of the original numbers there are in 1.
12
The final step in the derivation for the fractions-division rule is to consider dividing
something like 3 ÷ 4/5, which means “How many 4/5 are there in 3?” Well, we know how many
4/5 there are in 1, so shouldn’t there be 3 times as many 4/5 in 3 as in 1? When faced with 3 ÷
4/5, we might think of approaching this in two steps: First, note that there are 5/4 four fifths in 1.
Second, there must be 3 times as many 4/5 in 3 as in 1, or 3 x 5/4.
A Conceptual Lesson
Three Principles of Teaching for Conceptual Understanding of Mathematics
From the preceding lesson, I highlight three principles of teaching for conceptual
understanding of mathematics. After stating each principle, I relate the principle to the specific
example of fractions.
Principle 1: Teachers’ abilities to identify the main mathematical concepts that are
important for their students to learn and to understand those concepts are critical.
Two main mathematical concepts are demonstrated in the fractions-division example.
First, A ÷ B can be thought of as “How many Bs are there in one A?” This measurement
approach to division is applicable to division situations that would be much more difficult to
think about using only the partitive model of division.
Second, when multiplying or dividing fractions, one must attend to how the unit changes.
Students must think beyond 1/2 ÷ 1/3 as 1 with 1/6 left over. Before students can understand
fraction division, they must also be able to think of the 1/6 left over as 1/2 of a 1/3.
If teachers teaching division of fractions are aware of the role played by these two main
mathematical concepts, they can direct their students’ attention toward these ideas during the
lesson. If teachers do not make these ideas explicit, some students, but probably a small number,
may still pick up on the ideas. In such a case, neither the teacher nor the students will be aware
that the difference between those who understand and those who do not may lie in their
understanding of these ideas.
Principle 2: Teachers must provide opportunities for students to build on their existing
knowledge.
Teachers who understand the mathematics are in a position to think about their students’
understanding of the mathematics. There are two questions I ask myself as I consider ways to
tap into my students’ knowledge. First, what conceptual understanding do the students bring to
the task? In the example provided in this paper, I assume the adult students I am teaching can
apply procedures for operating on fractions and possess basic understanding of fraction concepts.
I do not assume that the students have a good understanding of the two main concepts mentioned
above: measurement division and the role of the unit. The lesson was designed to provide
teachers opportunities to consider those two concepts.
The other question I ask myself as I consider ways to tap into my students’ knowledge is
What real-life situations might be used that would be relevant to the students? After posing 1/2
– 1/3, I suggest the students think about pies. In the past I have suggested that they consider
pizzas, but I have found that many students view pizzas as precut into eighths, and this image
seems to interfere with learning. Given that pies are generally purchased uncut, students are
more comfortable imagining slicing a pie in any manner they choose.
Later in the lesson we dealt with recipes and cups of sugar. This example was chosen
because it provided a natural way for students to think about the unit changing. When
considering how many recipes requiring 1/3 cup of sugar might be made with 1/2 cup of sugar,
students can be asked to consider the remaining sugar in terms of cups (1/6 cup of sugar) and in
terms of recipes (1/2 a recipe). In so doing, the students have a context that makes explicit the
different units. Use of the context facilitated the following conversation with a student who had
Philipp
13
been asked how many recipes she could bake if each recipe required 1/3 cup of sugar and she
had 1/2 cup of sugar (the situational equivalent to “How many thirds are there in one half?”). (I
is the interviewer.)
St:
I have 1, with 1/6 left over.
I:
Consider the 1. What is the 1 a number of?
St:
One recipe.
I:
And the 1/6? What is it a number of?
St:
One-sixth recipe. No, 1/6 cup of sugar.
I:
So we know that you have enough sugar for 1 recipe, and you have some sugar
left over.
St:
Yes.
I:
Could the leftover sugar be used in another recipe?
St:
Um, I think so. Let’s see, it takes 1/3 cup of sugar for one recipe, and I have 1/6
cup of sugar left, so I could make another half.
I:
Half what? Half of a cup of sugar?
St:
No, half of a recipe.
I:
How can 1/6 of something also be 1/2 of something?
St:
One-sixth cup can be 1/2 of a recipe.
Consider a conversation without benefit of a context. The student had been asked, “How many
thirds are there in one half?"
St:
There is 1 third in 1/2, and there is 1/6 left.
I:
OK. Now the 1/6 left over, what is it 1/6 of?
St:
What do you mean? It is 1/6.
I:
Well, is it 1/6 of a whole, or a half, or a third?
St:
It is 1/6 of a whole.
I:
And the 1 third, when you write that as an answer, don’t you write that as 1?
St:
What do you mean?
I:
Well, suppose you wrote this problem as a division problem with 1/3 as the
divisor and 1/2 as the dividend, wouldn’t the quotient be 1?
St:
Yes.
I:
That 1 is 1 what?
St:
One third.
I:
And the left over 1/6. What is that?
St:
That is the remainder.
I:
Could you write it as a quotient?
St:
Yes, I suppose I could divide it by the divisor, the way I do with whole numbers.
(She does the calculations and gets 1/2).
I:
So what is your answer?
St:
One and a half.
I:
One and a half what?
St:
One and a half thirds.
Of course, the conversation may not go this way, but I have had similar conversations, and I find
that they are awkward because the units (the wholes and the thirds) keep getting lost during the
discussion. In fact, the student in the second vignette may not have conceptualized 1/6 as half of
1/3, but, instead, to get the 1/2 she may simply have applied a procedure that she remembered
using with whole numbers. A student who possesses a solid understanding of the concepts ought
to be able to make sense of these ideas whether or not they are embedded in a context. I see
using the context as a means of supporting students whose understanding is still fragile.
When considering situations that would be relevant to students, one must not, of course,
assume that a situation relevant to one student will be relevant to another. As a child, I was very
14
interested in baseball and teachers could have used a batter’s slump or hitting streak as a way to
help me think about proportional reasoning. This context would not have worked for someone
who had no interest in baseball. On one level, this seems obvious. Yet on another level, I think
teachers often gloss over the fact that when using contexts, some students are a step behind their
peers because they do not understand the context well enough to be able to move around flexibly
within it. Among elementary school teachers, there is a tendency to create contexts in class—but
secondary school mathematics teachers often do not feel that they have the luxury of taking the
time to develop meaningful contexts.
A Conceptual Lesson
Principle 3: Introduce symbols and procedures after students understand the concepts
these symbols and procedures are meant to represent.
There is a great deal of discussion in the United States today about whether the reform
documents, including the NCTM Standards (1989) and the California Framework (1992), have
gone too far in deemphasizing the teaching of skills and procedures6. I believe that the
discussion has gone in the wrong direction. The question should not be whether to teach
concepts or procedures. We need both. The question should be whether the order in which these
are taught makes any difference. Does it matter whether we teach the procedures first, or the
concepts? It turns out that it does. If we teach procedures before we teach the underlying
concepts, students are less likely to learn the concepts (Wearne & Hiebert, 1988). I will address
this issue with contrasting examples of a first grader and a fifth grader.
Once a week I teach a mathematics lesson in a first-grade classroom at a local public
school. In October I introduced fractions to the students by having them work with pattern
blocks as they constructed wholes using red trapezoids (halves), blue rhombi (thirds), and green
triangles (sixths). By the end of the lesson, some students were constructing wholes using
different-sized pieces. At this time we did not represent any of the fractions symbolically;
instead we just spoke about the fractions.
The very next day I was at my son’s soccer practice when a couple of mothers asked me
what I was doing in the first-grade class. Alyson, a student from the class, happened to be
standing close by, so I called her over. Alyson and I talked:
I:
Alyson, is a half and a half more than a whole, less than a whole, or equal to a
whole?
Al:
What does equal mean.
I:
Equal means “is the same as.”
Al:
It is equal to a whole.
I:
Is a third and a third more than a whole, less than a whole, or equal to a whole?
Al:
Less than a whole.
I:
How do you know?
Al:
Because you need another third to make it a whole.
I:
Is a half and a third more than a whole, less than a whole, or equal to a whole?
Al:
(After about 5 seconds): Less than a whole.
I:
How do you know?
Al:
Because you need another sixth to make it a whole.
6
It turns out that these documents have not had an important influence in affecting how
teachers teach. Jim Stigler, who coordinated the video study of the Third International
Mathematics and Science Study, found that although most of the American eighth-grade
mathematics teachers videotaped knew about and had read portions of reform documents,
most were teaching lessons that emphasized procedures and definitions, not conceptual
learning.
Philipp
15
I:
Alyson, how did you think about that question? Are you picturing something in
your mind?
Al:
A red and a green.
I:
You mean you know a red is a half and a green is a sixth?
Al:
Yes.
Notice how quickly Alyson was able to make the link between the physical model and the
fractional names. Our schools are filled with first graders who, if given the chance, are ready to
reason as Alyson did.
Recently I was being escorted to a class by a fifth grader who told me that his class had
been studying fractions, so I posed the same questions I had asked the first grader. Our
conversation went as follows:
I:
Jim, is a half and a half more than a whole, less than a whole, or equal to a whole?
Jim: Equal to a whole.
I:
Is a third and a third more than a whole, less than a whole. . . ?
Jim: (Interrupting) It is two sixths.
I:
Hm. That’s interesting. When I asked you what one half and one half was, you
said one whole, but when I asked about one third and one third, you said two
sixths.
Jim: Hm. Oh, ok, I see now.
I:
What is it that you see?
Jim: One half and one half is two fourths.
Unlike the first grader who had a way of picturing halves and thirds in her mind, Jim’s primary
way of thinking about these fractions was to consider the symbols and procedures. As a result,
he would manipulate the symbols in his head, but he had little experience developing number
sense to support his thinking.
We Teach What We Know
Thompson, Philipp, Thompson, and Boyd (1994) suggested that teachers’ orientations
toward mathematics and toward teaching mathematics are reflected in the kinds of questions they
pose and the kinds of conversations they strive to hold. Two teachers who value problem
solving may approach the same tasks differently because one teacher may possess a
calculational orientation whereas the other teacher may possess a conceptual orientation.
The actions of a teacher with a calculational orientation are driven by a fundamental
image of mathematics as the application of calculations and procedures for deriving
numerical results. This does not mean that such a teacher is focused only on
computational procedures. Rather, his view of mathematics is more inclusive but still one
focused on procedures—computational or otherwise—for “getting answers.” (Thompson
et al., p. 86)
A teacher who possesses a calculational orientation may view problem solving as an occasion to
solve problems, whereas a teacher who possesses a conceptual orientation will view problem
solving as an occasion for students to reason and to reflect on their reasoning.
A teacher with a conceptual orientation is one whose actions are driven by
° an image of a system of ideas and ways of thinking that she intends the students to
develop;
° an image of how these ideas and ways of thinking can develop;
16
° ideas about features of materials, activities, expositions, and students’ engagement with
them that can orient the students’ attention in productive ways . . . ;
° an expectation and insistence that students be intellectually engaged in tasks and
activities. (Thompson et al., p. 86)
A Conceptual Lesson
How does one develop a more conceptual orientation? Alba Thompson once suggested
that to help people think differently about mathematics, mathematics educators should consider
changing its name to Mathematical Arts. Teaching Mathematical Arts is fundamentally about
getting students to reason in particular ways and not about getting students to do particular
things. If teachers and students internalized this new view of mathematics, then the mathematics
classroom would become a place where doing would take the back seat to understanding and
calculating would take the back seat to sense making. Although a teacher possessing such a view
might not deeply understand everything she teaches, she would recognize that there is something
to be known. When we come to understand mathematics as a discipline about which we reason,
we are poised to recognize when we do not understand something deeply, which is the first step
toward developing a deeper understanding.
Lee Shulman (1986) wrote, “Those who can, do. Those who understand, teach.” Alba
Thompson’s research had gone a long way toward showing that we teach what we know and do
not teach what we do not know. So what are teachers to do when they find themselves in the
position of having to teach a topic that they do not understand deeply? There is no easy answer
to this question. Sowder, Philipp, Armstrong, and Schappelle (1998) found that after they
provided middle school teachers in-services during which the teachers had opportunities to
conceptualize the mathematics they were teaching, the teachers spoke critically of mathematics
in-services that did not focus on mathematics. I’ll end with one general suggestion: Let’s put the
mathematics back into teacher in-services.
Philipp
17
REFERENCES
Ball, D. L. (1990). Prospective elementary and secondary teachers’ understanding of division.
Journal for Research in Mathematics Education, 21, 132–144.
Borko, H., Eisenhart, M., Brown, C. A., Underhill, R. G., Jones, D., & Agard, P. C. (1992).
Learning to teach hard mathematics: Do novice teachers and their instructors give up too
easily? Journal for Research in Mathematics Education, 23(2), 194–222.
California Department of Education. (1992). Mathematics framework for California public
schools: Kindergarten through Grade Twelve. Sacramento, CA: Author.
Carpenter, T. P., Ansell, E., Franke, M. L., Fennema, E., & Weisbeck, L. (1993). A study of
kindergarten children's problem-solving processes. Journal for Research in Mathematics
Education, 24(5), 428–441.
National Council of Teachers of Mathematics. (1989). Curriculum and evaluation standards for
school mathematics. Reston, VA: Author.
Shulman, L. S. (1986). Those who understand: Knowledge growth in teaching. Educational
Researcher, 15 (2), 4–14.
Skemp, R. R. (1978). Relational understanding and instrumental understanding. Arithmetic
Teacher, 26, 9–15.
Sowder, J. T., Philipp, R. A., Armstrong, B. E., & Schappelle, B. P. (1998). Middle-grades
teachers' mathematical knowledge and its relationship to instruction: A research
monograph. Albany, NY: State University of New York Press.
Thompson, A. G., Philipp, R. A., Thompson, P. W., & Boyd, B. A. (1994). Calculational and
conceptual orientations in teaching mathematics. In D. B. Aichele & A. F. Coxford (Eds.),
Professional development for teachers of mathematics, (pp. 79–92). Reston, VA: National
Council of Teachers of Mathematics.
Wearne, D., & Hiebert, J. (1988). A cognitive approach to meaningful mathematics instruction:
Testing a local theory using decimal numbers. Journal for Research in Mathematics
Education, 19(5), 371–384.